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Another quick .NET triage/analysis of a related #PUBNUBRAT dropper/launcher (?) 1d155032232cd40c1788271546af36ec (U4.conf). This one we start immediately with extracting the 'app' resource using dnSpy to get 5bbe762b83e051776f1b5ea30ffc0050 (application/x-lzip). 
5bbe762b83e051776f1b5ea30ffc0050 decompressed to the goliath ~8MB ca19c3c3c2ef656b33d7173a49186f5a (application/x-dosexec) which is also a .NET binary. Back in dnSpy, which nearly chokes on the size, we finally get to a main decryption routine.
We could take the next steps of this in a million ways, but this is easy to do in @GCHQ's #CyberChef. First From Base64 & To Hex the Key and IV for the crypto routine and save these in hex.
This is malware analysis 101 for most folks, but I thought I'd share a quick thread on easy .NET analysis using a recent wave of a malicious xlsx downloading PUBNUBRAT. cc @issuemakerslab @blackorbird and @navSi16 who all tweeted about this in Jan. #threathunting #dfir
88017e9f2c277fa05ee07ecc99a0a2dc (홍삼6품단가 .xlsx) is a doc that has multiple follow-on payloads including 05683b9a13910d768b7982d013c31cb9 (U3.conf)... see also 홀리데이 와이퍼(Operation Holiday Wiper)로 귀환한 로켓맨 APT 캠페인 by @alac blog.alyac.co.kr/2089
05683b9a13910d768b7982d013c31cb9 (U3.conf) is a backdoor that uses the PubNub API (a legit service) for C2 (see @MITREattack's T1102). It's a .NET binary and without its config it doesn't do much a sandbox. How do you detect network C2 over PubNubApi?
